General Virus Information

• (1) Spreads itself from one file to another without your input or knowledge. Technically, this is known as self-replication and propagation.
• (2) Implements the symptom or damage planned by the perpetrator. This could include erasing a disk, corrupting your programs or just creating havoc on your computer. Technically, this is known as the virus payload which can be benign or malignant at the whim of the virus creator.

A malignant virus is one that attempts to inflict malicious damage to your computer, although the damage may not be intentional. There are a significant number of viruses that cause damage due to poor programming and outright bugs in the viral code. A malicious virus might alter one or more of your programs so that it does not work as it should. The infected program might terminate abnormally, write incorrect information into your documents. Or, the virus might alter the directory information on one of your system area. This might prevent the partition from mounting, or you might not be able to launch one or more programs, or programs might not be able to locate the documents you want to open.

Some of the viruses identified are benign; however, a high percentage of them are very malignant. Some of the more malignant viruses will erase your entire hard disk, or delete files.

The National Center for Computer Crime Data in Los Angeles estimates that American business have lost as much as $550 million from unauthorized access to computers yearly. The amount of lost time may be incalculable.

As an indication of the severity of the problem, the federal government has helped to form a virus SWAT team called the Computer Emergency Response Team. Its job is to investigate security threats in major computer networks across the country. The Software Publishers Association has also adopted certain measures to address the problem.

Furthermore, in the last year many Fortune-listed companies have begun to establish computer policies to deal with viruses. In many cases those new procedures will set practices for testing in all software before it is put on a network and restrict the downloading of software from electronic bulletin boards. Literally no one who uses computers--not the government nor the police nor even your local bank--is immune from computer viruses.

Suppose a space shuttle executed order from a virus-infected software program. Or an air traffic controller was given incorrect information from a fouled system. Or your company's financial records were suddenly eradicated or permanently altered.

These are not necessarily fantasies of impending doom. Thus far, computer viruses have hit a variety of systems, including Fortune 500 companies, government agencies, major universities, newspapers and large networks linking vast numbers of computers and huge volumes of information.

These are viruses that attach themselves to (or replace) .COM and .EXE files, although in some cases they can infect files with extensions .SYS, .DRV, .BIN, .OVL and .OVY.
With this type of virus, uninfected programs usually become infected when they are executed with the virus in memory. In other cases they are infected when they are opened (such as using the DOS DIR command) or the virus simply infects all of the files in the directory is was run from (a direct infector).

These are not necessarily fantasies of impending doom. Thus far, computer viruses have hit a variety of systems, including Fortune 500 companies, government agencies, major universities, newspapers and large networks linking vast numbers of computers and huge volumes of information.
Every logical drive, both hard disk and floppy, contains a boot sector.
This is true even of disks that are not bootable.
This boot sector contains specific information relating to the formatting of the disk, the data stored there and also contains a small program called the boot program (which loads the DOS system files).
The boot program displays the familiar "Non-system Disk or Disk Error" message if the DOS system files are not present.
It is also the program that gets infected by viruses. You get a boot sector virus by leaving an infected diskette in a drive and rebooting the machine. When the boot sector program is read and executed, the virus goes into memory and infects your hard drive.
Remember, because every disk has a boot sector, it is possible (and most common) to infect a machine from a data disk.
NOTE: Both floppy diskettes and hard drives contain boot sectors.

The first physical sector of every hard disk (Side Ø, Track Ø, Sector 1) contains the disk's Master Boot Record and Partition Table. The Master Boot Record has a small program within it called the Master Boot Program which looks up the values in the partition table for the starting location of the bootable partition, and then tells the system to go there and execute any code it finds. Assuming your disk is set up properly, what it finds in that location (Side 1, Track Ø, Sector 1) is a valid boot sector. On floppy disks, these same viruses infect the boot sectors.

You get a Master Boot Record virus in exactly the same manner you get a boot sector virus -- by leaving an infected diskette in a drive and rebooting the machine.
When the boot sector program is read and executed, the virus goes into memory and infects the MBR of your hard drive. Again, because every disk has a boot sector, it is possible (and common) to infect a machine from a data disk.